10. Water is being emptied out of a sink. The depth of water, \(y \mathrm {~cm}\), at time \(t\) seconds, may be modelled by
$$y = t ^ { 2 } - 14 t + 49 \quad 0 \leqslant t \leqslant 7$$
- Find the value of \(t\) when the depth of water is 25 cm .
- Find the rate of decrease of the depth of water when \(t = 3\).